The major long-term objective of these studies is to advance our understanding of placental development and function, particularly the cellular basis of trophoblast function. A critical event in trophoblast development is the differentiation of stem cell-like cytotrophoblast into the structurally and functionally mature syncytiotrophoblast. The central hypothesis of this proposal is that plasma membrane phospholipid (PL) metabolism plays a major role in trophoblast differentiation and function and that it is closely tied to the expression and function of cell surface adhesion molecules. This idea will be tested in three interrelated specific aims using the vitronectin receptor (VNR) as a model adhesion molecule. The studies take advantage of our ability to obtain pure cultures of cytotrophoblast and our ability to block or induce differentiation by manipulating culture conditions. Each aim is supported by preliminary data. Specific aim 1 examines the role of plasma membrane PL in trophoblast differentiation. Membrane PL content and asymmetry and the key metabolic pathways utilized by trophoblast will be examined. Anti- PL antibodies have been associated with recurrent pregnancy loss and it has been proposed hat they affect trophoblast differentiation. This hypothesis will be tested by examining the effects of aPL antibodies on normal trophoblast differentiation and function in vitro. Specific aim 2 explores the roles of VNR in trophoblast differentiation and function. The placenta is a rich source of this integrin but its role in trophoblast is not known. Changes in PL metabolism have been correlated with the attachment of cells to certain substrates and VNR activity is affected by membrane PL composition. VNR has also been implicated in cell fusion events. Its role in regulation of trophoblast differentiation and substrate attachment will be investigated and results correlated with the PL studies that comprise specific aim 1. Modulation of receptor expression by cytokines, growth factors and anti-PL antibodies will also be studied. Invasion of maternal spiral arteries suggest that an effective cell-cell adhesion system must exist to allow trophoblast cells to migrate along the endothelium. Little is known about trophoblast adhesion molecules, especially those mediating cell-cell adhesion. Specific aim 3 will characterize cell adhesion molecules involved in trophoblast-endothelial cell interaction in vitro and the effect of cytokines and aPL antibodies on this process. Together, the proposed studies should provide significant new information about cell membrane molecules that are critical to the regulation of trophoblast differentiation and function.